Dr. Susanne Henning, who led the study at UCLA, said: “It was known that green tea polyphenols are more effective and offer more health benefits than black tea polyphenols since green tea chemicals are absorbed into the blood and tissue.”

“Our new findings suggest that black tea, through a specific mechanism through the gut microbiome, may also contribute to good health and weight loss in humans.”

She said the results suggest both green and black teas are prebiotics, so encourage the growth of good bacteria in the gut that boosts a person’s wellbeing.

Experiments showed the percentage of bacteria linked to obesity decreased in mice given black and green tea.

And, bacteria that are linked to a lean body mass increased.

Past studies have shown the chemicals in green tea alter the metabolism in the liver.

But, the new findings show, the chemicals in black tea, which are too large to be absorbed in the small intestine, stimulate the growth of “good” gut bacteria, that in turn also affects the metabolism.

A month into the study, mice taking part were all weighed.

Mice given black or green tea extracts dropped the same amount of weight as those who ate a low-fat diet.

Dr. Zhaoping Li, the study’s senior author, said the benefits of green and black tea go beyond their antioxidant benefits.

“For black tea lovers, there may be a new reason to keep drinking it,” she said.